Implement a Unique Lines Command

Problem Statement

In Unix-like operating systems, the uniq utility reads an input stream of text lines and filters out adjacent duplicate lines.

Implement a generator function unique_lines that accepts an iterable of lines and yields the deduplicated stream according to the specified options.

Function Signature

from typing import Iterable, Iterator

def unique_lines(
    stream: Iterable[str],
    ignore_case: bool = False,
    show_count: bool = False
) -> Iterator[str]:
    pass

Requirements

1. Consecutive Deduplication: Only adjacent duplicates should be collapsed. Non-adjacent duplicates should still appear.
2. Case Sensitivity: If ignore_case is True, lines should be compared case-insensitively (e.g., "Foo" and "foo" are considered duplicates). However, the output line should preserve the exact casing of the first occurrence in the consecutive run.
3. Counts: If show_count is True, format the output string as "{count} {line}", where count is the number of consecutive occurrences of that line.
4. Streaming: The input stream may be arbitrarily large or infinite. Your implementation must process lines lazily with O(1) auxiliary space beyond storing the current line and count.

Constraints

• Line lengths: 0 <= len(line) <= 10^5 characters.
• Number of lines in stream: 0 <= N <= 10^7 (or unbounded stream).
• Auxiliary space complexity must be O(1) (excluding the yielded values).

Examples

Example 1

stream = ["apple", "apple", "banana", "apple"]
result = list(unique_lines(stream))
assert result == ["apple", "banana", "apple"]

Explanation: The first two "apple" lines are adjacent duplicates and collapse into one. The later "apple" is not adjacent to the previous ones, so it is preserved.

Example 2

stream = ["System", "system", "SYSTEM", "Error", "error"]
result = list(unique_lines(stream, ignore_case=True, show_count=True))
assert result == ["3 System", "2 Error"]

Explanation: "System", "system", and "SYSTEM" form a single run of 3 occurrences; the casing of the first line ("System") is retained. "Error" and "error" form a run of 2 occurrences.